Boiling water nuclear reactor and emergency core cooling system of the same

Abstract

A boiling water nuclear reactor comprises: a reactor containment vessel including a dry well and a wet well; a vent pipe connecting the dry well and the pressure suppression pool; a gravity-driven water injection pool to hold boric acid aqueous solution; an emergency core water-injection piping system for causing the boric acid aqueous solution in the gravity-driven water injection pool to fall so as to be injected into the reactor pressure vessel in case of reactor accident; a static containment vessel cooling system pool; a static containment vessel cooling system heat exchanger; a dry well connection pipe connecting an upper part of the static containment vessel cooling system heat exchanger and the dry well; and a gas vent pipe for discharging noncondensible gas in the static containment vessel cooling system heat exchanger into the inside of the pressure suppression pool.

Description

CROSS REFERENCES TO RELATED APPLICATIONS[0001]The present application is a Divisional of U.S. application Ser. No. 12 / 056,813, filed Mar. 27, 2008 which is based upon and claims benefit of priority from prior Japanese Patent Application No. 2007-87617, filed in the Japanese Patent Office on Mar. 29, 2007, the entire content of which is incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]This invention relates to a gravity-driven emergency core cooling system (ECCS) and also to a boiling water nuclear reactor (BWR) using the same.[0003]Studies are being made of introducing equipment that operates statically (passively), utilizing natural force, without using dynamic (actively) devices such as pumps mainly in order to raise the simplicity of safety equipment and improve the reliability of boiling water nuclear reactors. Among others, gravity-driven emergency core cooling systems (ECCS) are known for pouring water into the nuclear reactor in case of an accident as shown i...

AI Technical Summary

Problems solved by technology

When a loss-of-coolant accident (LOCA) occurs and the pipe connected to the reactor pressure vessel is ruptured in the inside of the dry well, the water level in the reactor pressure vessel falls.

On the other hand, when the isolation valve and / or the pressure-reducing valve of the gravity-driven water injection pipe become unopenable for some reason or another, there arises a situation where the core can no longer be cooled.

Then, the core can become damaged and molten.

Besides a LOCA, an anticipated transient without scram (ATWS) can take place to threaten the safety of nuclear reactor.

This is an incident where the attempt to insert the control rods fails partly or totally although a scram is required for the nuclear reactor in order to protect the core and the reactor containment vessel when an accident of total loss of water feed to the nuclear reactor or an incident of a total closure of the main steam isolation valve occurs.

In such a situation, there arises a possibility that the injection of boric acid aqueous solution has been completed before the injection of water by means of the gravity-driven ECCS is started to make it difficult to maintain the subcritical state so that the core may be plunged back into a critical state because the boric acid is diluted by about 1,500 m3 cold water injected by the gravity-driven ECCS.

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